In many system-on-chip (SOC) applications, an oscillator is a very important module. The oscillators are classified into resistance-capacitance oscillators—i.e. RC oscillators, inductance-capacitance oscillators—i.e. LC oscillators, crystal oscillators, tuning fork oscillators, and the like. The RC oscillator outputs an oscillation signal through charging and discharging the capacitor, and it can adjust the frequency of the oscillation signal by adjusting the resistance or capacitance. With respect to other types of oscillators, the RC oscillator has the advantages of simple structure and high precision. Therefore, the on-chip RC oscillator (RC silicon oscillator) is widely used in charge pump (PUMP) driving, a logic (LOGIC) clock, and other applications in a smart card, an Micro Control Unit (MCU) and other products.
The temperature coefficient of frequency of the RC oscillator is determined by the temperature coefficient of the product RC, wherein the temperature coefficient of R, i.e. the resistance itself, is the main factor. The resistor after the temperature coefficient compensation provides the possibility for the realization of the project of the high-precision RC oscillator. In the prior art, the resistor circuit with temperature coefficient compensation is achieved mainly by interconnecting in series the resistors having a positive or negative temperature coefficient, or by interconnecting in parallel the resistors having a positive or negative temperature coefficient. As shown in FIG. 1, there is a resistor circuit with temperature coefficient compensation. In FIG. 1, a series resistor R101 is formed by interconnecting in series a resistor Rp101 having a positive temperature coefficient and a resistor Rn101 having a negative temperature coefficient, with the temperature coefficient of the entire series resistor R101 reduced or eliminated by mutually offsetting and compensating the positive and negative temperature coefficients of the resistors Rp101 and Rn101. In the application of the on-chip RC oscillator, with the two series resistors Rp101 and Rn101 having the on-chip structure, different types of resistors are needed for the on-chip resistor to achieve a resistor having a different temperature coefficient; for example, a polysilicon resistor, a diffusion resistor or an N-well resistor can achieve a positive temperature coefficient; and a polysilicon resistor can achieve a negative temperature coefficient. The positive or negative temperature coefficient of the polysilicon resistor can vary with different doping concentration thereof. In semiconductor manufacturing, the resistance value may changes about ±20% under different process variations, i.e. process corner. For example, the resistance value will be smaller under faster process and larger under slower process. The change directions of different types of resistors may be different. Thus, the resistance values of different types of resistors many become larger or smaller. Due to the different types of resistors Rp101 and Rn101 connected in series, one of the resistance values of the two resistors may become larger while the other one of the resistance values may become smaller. The structure as shown in FIG. 1 will not play a role of temperature compensation unless the resistance values of the two resistors become larger or smaller at the same time. If one of the resistance values becomes larger while the other one of the resistance values becomes smaller, the structure as shown in FIG. 1 has no compensating effects and even deteriorates the compensating effect.
Similar to the resistor circuit with temperature coefficient compensation formed in series, because the process corners of the two resistors are not necessarily changed in the same direction in the case that the two parallel resistors are different in types, the resistor circuit with temperature coefficient compensation formed in parallel has no compensating effects and even deteriorating the compensating effect in the case of opposite corner changes.